$(function(){
  console.log('hello world!');
  let $btn = $('input'),
      num = window.localStorage.getItem('num')||0;

  $btn.val(`按了${num}次`);

  $btn.click(()=>{
    num++;
    window.localStorage.setItem('num',num);
    $btn.val(`按了${num}次`);
  })
});
